Hydrogen sulfide is a toxic, corrosive, flammable gas that causes problems in both the upstream and downstream oil and gas industry. Exposure to this gas, even at low concentrations, can cause serious injury or death. Hydrogen sulfide (H2S) in natural gas and crude oil reserves is often accompanied by small amounts of mercaptans (RSH), sulfides (R2S), polysulfides, and carbonyl sulfide (COS). Considerable expense and effort are expended annually to reduce the H2S content of gas and oil streams to make them suitable for commercial use.
Hydrogen sulfide has an offensive odor, and natural gas and crude oil streams containing substantial amounts of H2S are considered “sour.” In addition to natural gas and petroleum, there are also aqueous fluids that must be treated to reduce or remove H2S, such as waste water streams. Treatments to reduce or remove H2S from hydrocarbon or aqueous streams are referred to as “sweetening” treatments because the odor of the processed products is improved by the absence of hydrogen sulfide. A chemical compound that is used to remove or reduce H2S levels sometimes is called a “scavenger” or “scavenging agent.” Scavengers that react irreversibly with hydrogen sulfide or other sulfur species and convert them to a more inert form are considered nonregenerative.
In large production facilities, the most economical solution to remove H2S from a sour gas stream is to install a regenerative system. These systems typically employ a compound used in an absorption tower to contact the produced fluid and form weakly bound soluble salts which become unstable at elevated temperatures. The absorption compound, usually alkanolamines such as N-methyldiethanolamine (MDEA), and H2S are then regenerated by various means using heat, pressure reduction, or a combination thereof. The absorption material is reused in the system, and the separated H2S is treated by a modified Claus process to form elemental sulfur.
For hydrocarbon streams with small concentrations of hydrogen sulfide, the use of scavengers in batch treatments and continuous injection processes can provide a cost-effective alternative to conventional gas/liquid sweetening processes. Known hydrogen sulfide scavengers include solid scavengers (e.g. zinc-based or iron-based materials), oxidizing chemicals (e.g. chlorites, nitrites, bromates, iodates, and peroxides), aldehydes (e.g. formaldehyde, glutaraldehyde, acrolein, and glyoxal), reaction products of aldehydes and amines (e.g. triazines), metal carboxylates and other chelates, and other amine based products (e.g. amidines, maleimides, and amine oxides). (See Production Chemicals for the Oil and Gas Industry, CRC Press, 2010, Chapter 15, “Hydrogen Sulfide Scavengers,” pg. 363-375).
Although the application of hydrogen sulfide scavengers is widely practiced in production and processing operations in the oil and gas industries, known scavengers have one or more limitations ranging from exorbitant prices to health, safety, and environmental problems. Thus, a continuing need exists for alternative hydrogen sulfide scavengers that overcome these deficiencies.